1. Technical Field
The present invention relates to a board, more specifically to a noise reduction board that can reduce electromagnetic interference noise by use of an electromagnetic bandgap structure.
2. Background Art
As the operating frequencies of electronic products become higher, electromagnetic interference (EMI) has become a chronic noise problem. Particularly, as the recent electronic products are operated in a double-digit MHz to a few GHz, the EMI problem has become increasingly serious, making it urgent to find a solution. Among the EMI problems in a board, there have been few studies targeted for the noise occurred at an edge of the board, limiting the ability to shield the noise completely on the board.
An EMI noise refers to a noise that causes a noise problem generated by interference when electromagnetic waves generated in one electronic circuit, device or part is transferred to another electronic circuit, device or part. The EMI noise can be mainly classified into a radiation noise (see reference numerals 10 and 30 in FIG. 1) and a conduction noise (see reference numeral 20 in FIG. 1).
In the case of the radiation noise 10 that is radiated through an upper part of the board (i.e., a surface on which an electronic part is mounted), the noise problem is commonly solved by shielding the upper part of the board with an electromagnetic shielding cap, such as a metal cap. However, there have been insufficient studies for an effective solution for the radiation noise 30 (simply referred to as “edge noise”), which is the conduction noise 20 flowing through the inside of the board that is conducted to an edge of the board and radiated to the outside of the board.
FIG. 2 shows a briefly-modeled package board to show how the EMI noise is radiated, wherein the distributed dots indicate the spatial distribution of the intensity of E-field. It can be seen that the E-field is freely radiated through the edge of the board.
If it becomes possible to reduce the edge noise at the edge of a board by simply modifying the structure of the board, it is expected to dramatically save the development time and cost from the conventional solution using the metal cap or circuit. Moreover, it would be more advantageous in terms of spatial utilization or power consumption, and the noise in the frequency band above several GHz would be also removed easily, thereby effectively solving the EMI noise problem at the edge of the board.